Method and apparatus for providing welding type power

ABSTRACT

A welding-type power supply includes a controller, a preregulator, a preregulator bus, and an output converter. The controller has a preregulator control output and an output converter control output. The preregulator receives a range of inputs voltages as a power input, and receives the preregulator control output as a control input, and provides a preregulator power output signal. The preregulator includes a plurality of stacked boost circuits. The preregulator bus receives the preregulator output signal. The output converter receives the preregulator bus as a power signal and receives the output converter control output as a control input. The output converter provides a welding type power output, and includes at least one stacked inverter circuit.

RELATED APPLICATIONS

This is a continuation of, and claims the benefit of the filing date of,U.S. patent application Ser. No. 13/839,235, filed on Mar. 15, 2013which issued as U.S. patent Ser. No. 10/112,251 on Oct. 30, 2018.

FIELD OF THE INVENTION

The present disclosure relates generally to the art of welding typepower supplies. More specifically, it relates to welding type powersupplies that include multiple power processing circuits, such as aninverter type power supply. It has features and controls that allow itto be reconfigured as part of a modular welding type power supplysystem.

BACKGROUND OF THE INVENTION

There are many known types of welding-type power supplies. Welding-typepower, as used herein, refers to power suitable for electric arcwelding, plasma arc cutting or induction heating. Welding type system,as used herein, is a system that can provide welding type power, and caninclude control and power circuitry, wire feeders, and ancillaryequipment. Welding-type power supply, as used herein, is a power supplythat can provide welding type power.

Providing welding-type power, and designing systems to provide weldingtype power, provides unique challenges. Welding type systems will oftenbe moved from one location to another, and be used with differentinputs, such as single or three phase, or 115V, 230V, 460V, 575V, etc.,or 50 hz or 60 hz signals. Power supplies that are designed for a singleinput cannot provide a consistent output across different inputvoltages, and components in these power supplies that operate safely ata particular input level can be damaged when operating at an alternativeinput level. Also, power supplies for most fields are designed forrelatively steady loads. Welding, on the other hand, is a very dynamicprocess and numerous variables affect output current and load, such asarc length, electrode type, shield type, air currents, dirt on the workpiece, puddle size, weld orientation, operator technique, and lastly thetype of welding process determined to be most suitable for theapplication. These variables constantly change, and lead to a constantlychanging and unpredictable output current and voltage. Power suppliesfor many fields are designed for low-power outputs. Welding-type powersupplies are high power and present many problems, such as switchinglosses, line losses, heat damage, inductive losses, and the creation ofelectromagnetic interference. Accordingly, welding-type power supplydesigners face many unique challenges.

Additionally, welding-type power supplies or systems are often sold forone or more particular processes, such as stick, TIG, MIG, pulse,sub-arc, heating, cutting, and the maximum output power or current canbe anywhere from one hundred or less amps, to five hundred or more. Themaximum output of a particular welding-type system is chosen for theprocess and/or commercial market for which it is intended. While weldingtype power is a high power level, some welding type systems must providepower and/or output current than others. For example, the requiredoutput of a 300 amp stick welding system is different from the requiredoutput of a 600 amp MIG welding system.

Prior art welding type systems have typically been designed for aparticular output, and the power circuitry, controller, outputcircuitry, etc., are designed with the maximum output power in mind. A100 amp system might be different from a 200 amp machine, which isdifferent from a 300 amp machine and so forth. Thus, a welding typesystem is often designed from the ground up. Other times, in an effortto reduce the attending engineering costs, a welding-type power supplyis scaled up for a higher output by increasing switch capacities, orplacing switches in parallel. However, there are limits to this sort ofscaling up, and it gets ever more costly for components to tolerate evergreater currents. Both of these approaches in designing new welding typesystems required extensive design, engineering, and testing, and werethus relatively expensive.

U.S. Pat. No. 6,713,721 (hereby incorporated by reference), entitledMethod of Designing and Manufacturing Welding-Type Power Supplies,issued to Albrecht on Mar. 30, 2004, teaches to use a single powertopology with a given output current, and then to place modules inparallel as needed to obtain a desired output current. For example, ifeach module produces 250 amps, and 750 amps is needed, then threeparallel modules are used. While using modules in parallel as taught inU.S. Pat. No. 6,713,721 provides for increased output current, theoutput voltage for multiple modules is no higher than the output voltagefor a single module.

One prior art welding type power supply that is well suited forportability and for receiving different input voltages is a multi-stagesystem with a preregulator to condition the input power and provide astable bus, and an output circuit that converts or transforms the stablebus to a welding-type output. Examples of such welding-type systems aredescribed in U.S. Pat. No. 7,049,546 (Thommes) and U.S. Pat. No.6,987,242 (Geissler), and US Patent Publication 20090230941 (Vogel), allthree of which are owned by the owner of this disclosure, and herebyincorporate by reference. Miller® welders with the Autoline® featureinclude some of the features of this prior art.

There are many types of welding type power supplies that can provide awelding type power output from an AC or DC source of power. One generalcategory of power supply is known as a switched-mode power supply thatutilizes power semiconductor switches to chop a DC source of power andconvert this chopped power to a voltage and/or current suitable forwelding.

One type of switched-mode power supply is commonly known in the weldingindustry is an inverter type power supply. An inverter type power supplychops the source of DC power and applies it to the primary of atransformer. The frequency of the chopped voltage is typically muchhigher than the AC line frequency (50 to 60 Hz), commonly used as asource of power. Typical switching frequencies are in the range of 20KHz to 100 KHz. This higher frequency allows the inverter transformer tobe much small than a comparable line frequency transformer. Thesecondary of the transformer transforms the chopped voltage to a voltageand current level suitable for welding. Typically the secondary of thetransformer is connected to a rectifier and converted to DC and fed to asmoothing inductor to filter the output. This smoothed output is thenused as the output of the welding type power supply. For some weldingtype power sources the DC output is further processed and converted toan AC welding type output such as for AC GTAW.

There are many circuit topologies that can be used for an inverter basedwelding type power supply. Amongst these are topologies commonly knownas forward circuit, full-bridge, half-bridge, flyback, and others. Thesource of DC power for these types of power supplies is typicallyderived by rectifying a source of AC line power. An inverter type powersupply may also include a pre-regulator circuit following the rectifierand preceding the inverter circuit. The pre-regulator circuit can servethe function of providing a regulated DC bus voltage to the invertercircuit that may be at a voltage level different from the raw rectifiedAC voltage. This pre-regulator circuit may also include a power factorcontrol that can be used to improve the power factor of the currentdrawn from the AC line.

FIG. 1 shows a simplified schematic for an inverter based welding typepower supply consistent with those shown in U.S. Pat. Nos. 7,049,546 and6,987,242. AC line voltage is rectified, shown with three phase AC,could alternately be single phase. Typical values for AC line voltagecan range from 115 VAC or lower to 600 VAC. The inverter power supplymay be designed for a single nominal AC line voltage or for a range ofAC line voltages. The rectifier may include a filter capacitor, shown asC3, and provide an output voltage (Vrectified).

A pre-regulator may be included to provide a regulated bus voltage(Vbus) which may be regulated to a voltage greater than the peak of therectified AC line voltage. The pre-regulator circuit may also contain apower factor correction circuit or control to improve the power factorfor the current or power drawn from the AC line. FIG. 1 shows a boostconverter circuit arrangement for the pre-regulator. The switching ofpower semi-conductor Z3 is controlled by the gate drive signal providedby the pre-regulator/inverter control. The switching of Z3 can becontrolled in such a manner to provide a regulated Vbus as well asperform power factor correction.

The inverter topology shown is a half-bridge circuit with the primary ofthe high frequency inverter transformer, T1, connected between thecenter point of capacitors C1 & C2 and the junction between powersemiconductor switches Z1 & Z2. Power semiconductor switches areswitched on and off by a gate drive circuit which is shown as part ofthe inverter control. The switching frequency and ON/OFF ratio (or dutycycle, D) of the power semiconductor switches is controlled by theinverter control to provide a regulated output voltage and/or current ofthe welding type power supply. Z1 & Z2 alternately chop the DC busvoltage and create a high frequency AC voltage on the primary of thetransformer. For the half-bridge circuit shown the bus voltage is splitin half by the two capacitors, so effectively when either Z1 or Z2 isswitched on, one half of Vbus is applied across the primary of thetransformer. The transformer transforms the voltage to a level suitablefor welding. The center tapped secondary of the transformer is connectedto a diode rectifier (D2, D3) which rectifies the secondary highfrequency AC voltage to create a DC output. The DC output is filtered byinductor L1 to provide a smoothed output current to a welding arc.Additional components and circuits not shown in FIG. 1 may be includedsuch as snubbers and pre-charge circuits, EMI filters, gate drivecircuits, control power supplies and various other circuits.

A current sensor (CS1) provides a feedback signal indicative of theoutput current (I_out). Voltage feedback is also provided to theinverter control circuit, V_out. The inverter control may also provideother functions such as monitoring thermal sensors, controlling coolingfans, receiving and sending various status and control signals to othercircuits and controls such as a welding control. The weld controllershown allows the user to select and control a welding process, and mayprovide various signals, indicators, controls, meters, computerinterfaces, etc. to allow the user to set up and configure the weldingtype power supply as required for a given welding process. The weldcontroller typically will provide a command signal to the invertercontrol, indicated as I_ref. This command signal may be an outputcurrent level for the power supply or may be a more complex waveform orsignal dependant on the particular weld process and user inputs, voltageand current feedback signals and other conditions at the welding arc.Voltage feedback, current feedback, and other signals may be provided tothe weld control.

Welding type power supplies such as shown in FIG. 1 are often designedto operate from industrial level AC power such as 230, 460 or 575 VAC.As such the bus voltage Vbus may be greater than 900 Volts. This levelof bus voltage may require power semiconductor switches (Z1,Z2,Z3) thathave voltage ratings on the order of 1200 Volts. Circuits such assnubbers, slow voltage transition (SVT) or other circuits may berequired to reduce switching losses within the power semiconductorsbecause of the bus voltage level. In addition a series arrangement ofbulk capacitors (C1,C2) may be required to attain sufficient voltagerating. These capacitors may not share the voltage perfectly and end upwith a mismatch voltage level.

Welding type power supplies are often designed with components that canhandle the full range of input voltage and power and provide a givenwelding type power output. This may not be optimum for certainapplications, making the welding type power supply more complex orexpensive than may be necessary.

It can be desirable to have a welding type power supply that can handlea range of inputs such as illustrated above, yet use lower voltage powersemiconductors which may switch more efficiently and reduce or eliminatethe need for snubbers and other circuits to reduce switching losses. Itcan also be desirable to maintain a well balanced sharing of voltage forbus capacitors when a series arrangement is used. It can also bedesirable to provide a welding type power supply that can be readilyadapted for different input voltages and power levels along with variouswelding outputs.

Accordingly, a welding-type system having a power topology comprised ofa modular system, preferably one that can provide a desired outputcurrent greater than the output of any one module, and/or an outputvoltage greater than the output voltage of any one module is desired.Preferably, the system maintains the advantages of prior art portable,universal input systems, but also avoids some of the deficiencies of theprior art is desired.

SUMMARY OF THE PRESENT INVENTION

According to a first aspect of the disclosure a welding-type powersupply includes a controller, a preregulator, a preregulator bus, and anoutput converter. The controller has a preregulator control output andan output converter control output. The preregulator receives a range ofinputs voltages as a power input, and receives the preregulator controloutput as a control input, and provides a preregulator power outputsignal. The preregulator includes a plurality of stacked boost circuits.The preregulator bus receives the preregulator output signal. The outputconverter receives the preregulator bus as a power signal and receivesthe output converter control output as a control input. The outputconverter provides a welding type power output, and includes at leastone stacked inverter circuit.

According to a second aspect of the disclosure a welding-type powersupply includes a controller, a preregulator, a preregulator bus, and anoutput converter. The controller has a preregulator control output andan output converter control output. The preregulator receives a range ofinputs voltages as a power input, and receives the preregulator controloutput as a control input, and provides a preregulator power outputsignal. The preregulator includes a stacked boost circuit. Thepreregulator bus receives the preregulator output signal. The outputconverter receives the preregulator bus as a power signal and receivesthe output converter control output as a control input. The outputconverter provides a welding type power output, and includes at leastone stacked inverter circuit.

The controller includes a bus voltage balancing module in anotherembodiment. The bus voltage balancing module includes one or both of anintegrator and an accumulator in various embodiments, and/or receivesfeedback from the pre-regulator and output converter in variousembodiments.

According to a third of the disclosure a welding-type power supplyincludes a controller, a preregulator, a preregulator bus, and an outputconverter. The controller has a preregulator control output and anoutput converter control output. The controller includes a bus voltagebalancing module, and the preregulator control output is responsive tothe bus voltage balancing module. The preregulator receives a range ofinputs voltages as a power input, and receives the preregulator controloutput as a control input, and provides a preregulator power outputsignal. The preregulator provides a preregulator output signal andprovides feedback to the bus voltage balancing module. The preregulatorincludes at least one stacked boost circuit. The preregulator busreceives the preregulator output signal. The output converter receivesthe preregulator bus as a power signal and receives the output convertercontrol output as a control input. The output converter provides awelding type power output, and includes at least one stacked invertercircuit.

The preregulator bus is voltage regulated in one embodiment.

The output converter includes a dual stacked inverter in anotherembodiment.

The plurality of stacked boost circuits is a dual stacked boost circuit,a triple stacked boost circuit, or more than three stacked boostcircuits in various embodiments.

The controller includes a current balance module and/or an outputconverter flux balancing module in various embodiments.

The controller includes a start up module and/or a power down module inother embodiments.

The controller includes a power circuit configuration detection module,and one or both of the preregulator control output and the outputconverter control output are responsive to the power circuitconfiguration detection module in another embodiment.

The welding-type power also has a user-notification module responsive tothe power circuit configuration detection module and an auxiliary powercircuit detection module in another embodiment.

The welding-type power supply also includes a synthetic auxiliary acpower circuit having an ac adjustable frequency auxiliary power outputand/or a variable speed cooling fan receives auxiliary power output andblows air toward at least part of the preregulator and the outputconverter in another embodiment.

The output converter includes a stacked full bridge inverter in anotherembodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic for a prior art inverter based welding type powersupply;

FIG. 2 is a dual stacked boost pre-regulator power circuit in accordancewith the preferred embodiment;

FIG. 3 is a single stacked boost pre-regulator power circuit inaccordance with the preferred embodiment;

FIG. 4 is a dual stacked full bridge inverter output converter inaccordance with the preferred embodiment;

FIG. 5 is a stacked full bridge inverter output converter in accordancewith the preferred embodiment;

FIG. 6 is a block diagram of a welding-type power supply in accordancewith the preferred embodiment;

FIG. 7 is a controller for a pre-regulator in accordance with thepreferred embodiment;

FIG. 8 is a controller for a stacked boost pre-regulator circuit inaccordance with the preferred embodiment;

FIG. 9 is a control loop for a dual stacked boost pre-regulator circuitin accordance with the preferred embodiment;

FIG. 10 is a controller for an inverter-based output converter inaccordance with the preferred embodiment;

FIG. 11 is a controller for an inverter-based output converter inaccordance with the preferred embodiment;

FIG. 12 shows four PWM signals for the inverter-based output converterin accordance with the preferred embodiment; and

FIG. 13 is a control loop for an inverter based output converter inaccordance with the preferred embodiment;

Before explaining at least one embodiment of the method and system indetail it is to be understood that the disclosure is not limited in itsapplication to the details of construction and the arrangement of thecomponents set forth in the following description or illustrated in thedrawings. The method and system is capable of other embodiments or ofbeing practiced or carried out in various ways. Also, it is to beunderstood that the phraseology and terminology employed herein is forthe purpose of description and should not be regarded as limiting. Likereference numerals are used to indicate like components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the method and system will be illustrated with reference toparticular circuits and topologies it should be understood at the outsetthat the method and system can be implemented with other circuits andtopologies.

Generally, the method and system include a welding type power supplywith a dual stacked boost pre-regulator circuit and a dual stacked fullbridge inverter circuit output converter. Stacked boost circuit, as usedherein, is a boost circuit including two switches, two diodes, and twocapacitors in a series arrangement, wherein the collector of one switchis connected to the emitter of the other switch, and each switch has aninductor associated therewith. Each switch is clamped to its associatedbus capacitor by the series arrangement with the diodes. A singlestacked boost may have one inductor connected to either the upper orlower switch. A dual boost preferably has an inductor with each switchso that the current can be balanced between the two upper branches, andlikewise for the two lower branches. Stacked boost circuit can havegroups of parallel switches. If a MOSFET switches are used, they areconnected drain to source, and if other switches are used they areconnected in like manner. FIG. 3 shows a stacked boost circuit. Stackedinverter circuit, as used herein, is two inverter circuits with theprimary side switches connected in series. A single stacked invertercircuit is an arrangement of at least one switch connected to a lowerbus and at least one switch connected to an upper bus driving at singletransformer.

One configuration of the welding type power supply consists of a singlestacked boost pre-regulator circuit to provide a lower powerconfiguration for the pre-regulator circuit. Another configuration ofthe welding type power supply consists of a single stacked full bridgeinverter circuit to provide a lower power configuration for the inverterpower circuit. A controller is provided to control the operation of thepre-regulator and output circuits. Controller, as used herein, is thedigital and/or analog circuitry and/or logic/instructions that cooperateto provide control signals to one or more circuits. A controller can belocated on a single board, or distributed across multiple locations.Dual stacked boost circuit, as used herein, is two stacked boostcircuits connected in parallel, with a common output bus, also fed froma common input rectifier. Alternatives include two rectifiers fed from acommon AC source, and/or two separate output busses. Output converter,as used herein, is power circuitry that receives an intermediate signalsuch as a bus and provides an output power signal. Output convertercontrol output, as used herein, is a control output used to control oneor more switches in an output converter, and can be comprised ofmultiple control signals. Preregulator, as used herein, is a powercircuit that receives input power one form, and provides it in anotherform to another power processing circuit. Preregulator bus, as usedherein, is the bus that is the output of a preregulator. Preregulatorcontrol output, as used herein, is a control output used to control oneor more switches in an preregulator, and can be comprised of multiplecontrol signals. Preregulator output signal, as used herein, is thepower output of a preregulator.

The controller provides various control algorithms and features.Preferably, it includes a plug and play module that can detect the powercircuit configuration and adapt or modify the control as required,provide status information to the user as to the detected configurationand possible operation outside of the intended parameters, detectoptional power supplies and adapt or modify a control based on thepresence of these supplies (example: 115 VAC aux. power circuit, wirefeeder power supply, etc.). Power circuit configuration detectionmodule, as used herein, is a control module that detects theconfiguration of a power supply, such as whether a single or dualstacked boost circuit is being used. Module, as used herein, is softwareand/or hardware that cooperates to perform one or more tasks, and caninclude digital commands, control circuitry, power circuitry, networkinghardware, etc.

Also, the system preferably includes a module for actively balancing abus voltage shared between two or more series capacitors, such as anaccumulator or integrator function, to accumulate a bus voltagedifference, with coordination of bus balancing between pre-regulator andinverter or other circuits.

The system preferably includes a module for actively balancing currentflow for a dual boost configuration and/or a module for coordinating andcontrolling start up and shut down of aux. power supplies, and/or activeflux balancing for the inverter circuit to reduce the likelihood oftransformer saturation, and/or a module for providing variable speed fanfor cooling, and/or a module for providing various self checks to assureproper operation of the pre-regulator and inverter circuits.

A dual stacked boost pre-regulator power circuit is illustrated in FIG.2. The output of the pre-regulator circuit shown is a regulated busvoltage indicated as Vbus. The bus voltage is shared approximatelyequally between two series capacitors C1 and C2. Vbus_top & Vbus_bottomrepresent the two capacitor voltages. Capacitors C1 and C2 may each becomprised of a single capacitor or multiple capacitors forming acapacitor bank. The input to the pre-regulator circuit is provided by arectifier that converts AC line voltage to a rectified DC voltage. Therectifier may be supplied with a range of line voltages (ex. 230 VAC,460 VAC, 575 VAC) and operate on either single or three phase. Range ofinputs voltages, as used herein, is a range spanning at least twoutility voltages.

The pre-regulator circuit may be designed to operate over a continuousspan of input voltage and provide an output bus voltage that isregulated at an approximately constant voltage that is greater than thehighest rectified voltage (ex. 920 VDC). Alternately, the pre-regulatormay provide a bus voltage that is at a level such that at some AC linevoltages the pre-regulator shuts down and passes the rectified linevoltage without further boosting (ex. may stop boosting when linevoltage reaches 575 VAC+15%). Also, the pre-regulator may be providedwith any source of DC voltage such as from a battery or generator. Insome cases AC line voltage may be provided by a generator, alternator orutility power. The preregulator preferably provides a voltage regulatedbus. Voltage regulated bus, as used herein, is a bus regulated to adesired voltage or voltage waveform.

The pre-regulator circuit shown in FIG. 2 is comprised of two boostcircuits with series connected switches (dual stacked boost). The firstboost circuit is comprised of series switches Z4,Z5, diodes D5,D6,inductors L7,L8 and current sensor CS7. Alternately an additionalcurrent sensor may be provided in series with inductor L8. The magnitudeof the current flowing in L8 may be calculated or inferred from thecurrent flowing in the other inductors (L7,L9,L10) and as such thisadditional current sensor may not be required. Alternatives provide forusing two, three, four or more stacked boost circuits in parallel.Plurality of stacked boost circuits, as used herein, is two or morestacked boost circuits arranged in parallel.

Switches Z4 & Z5 are controlled and switched ON & OFF at a switchingfrequency (10 Khz to 20 Khz or more, e.g.) with the ON time controlledor modulated by a control circuit as required to regulate the busvoltage while also controlling and regulating the current flowing in theinductors L7 & L8. Two pulse width modulation signals are provided tocontrol Z4 & Z5 independently (PWM1 & PWM2). In general, control ofthese switches is similar to the well known boost circuit shown in FIG.1, other than it may be desirable to phase stagger the two PWM signalsor interleave the switching signals. Interleaving has a benefit ofeffectively doubling the ripple current frequency present in theinductors L7 & L8, which may allow reduction of the switching frequencyof Z4 & Z5, reduce the filtering requirements and relative size of L7 &L8, along with other benefits. Other modifications of PWM1 and/or PWM 2may be implemented as described in more detail below to provide busvoltage balancing and current balancing with a second boost circuit. Theseries arrangement of Z4 & Z5 along with diodes D5 & D6 result in avoltage impressed across these devices that is approximately one halfVbus. This may allow more efficient devices to be used and reduce oreliminate the need for snubbers, SVT or other circuits to reduceswitching losses.

A second boost circuit is comprised of switches Z6,Z7 diodes D7,D8,inductors L9,L10 and current sensors CS9,CS10. The second boost outputis connected in common with the first boost circuit to Vbus. The inputis provided from a common rectifier. Alternately the second boostcircuit may receive its input from a separate rectifier or other sourceof DC power. Switches Z6 & Z7 are controlled by two additionalindependent PWM signals (PWM3, PWM4). These two PWM signals may besimilar to the two PWM signals provided to the first boost circuit. PWM3& PWM4 may be interleaved in a similar fashion as PWM1 & PWM2. Operationof the second boost circuit is similar to operation of the first boostcircuit. A more detailed description of the derivation and control ofthe four PWM signals is provided below. The dual boost circuit providesadditional power flow through the pre-regulator by sharing the currentflowing into Vbus, when compared to a single boost circuit.

A single stacked boost circuit arrangement for the pre-regulator isshown in FIG. 3. The description and operation is similar to thedescription given above for the first boost circuit as part of the dualboost arrangement. The control signals PWM1 & PWM2 are similar and maybe interleaved as described above. Modification of PWM1 & PWM2 may beimplemented to achieve bus voltage balancing. Modification of PWM1 &PWM2 for current balancing with a second boost however would not berequired because there is no second boost circuit present. The controlalgorithm or circuit may be modified to eliminate the current balancingmodification. As such it may be beneficial and desirable for a controlto detect the configuration of the pre-regulator circuit (single boost,dual boost) so that control modifications may be automaticallyimplemented. In general this arrangement of single boost compared todual boost may reduce the total output boost current flowing into the DCbus such that this arrangement is suitable for a lower power weldingpower supply, or a welding power supply that can only operated from areduced range of input voltages (ex. 400-600 VAC, vs. 230-600 VAC for adual boost). This may allow a circuit with reduced complexity and costfor some applications that don't require a full range of input voltagesfor example. It may also be desirable to detect the pre-regulatorarrangement (single boost, dual boost) and provide feedback to the uservia an indicator, user interface, or other means as to the arrangementand the capability of this arrangement. For example a customer with asingle boost arrangement may be alerted to an incorrect line voltage ifthe welding type power supply is connected to 230 VAC, and the singleboost range is intended to be 400-600 VAC. It may therefore be desirableto detect the pre-regulator configuration to allow variousconfigurations of welding type power supplies to be manufactured, toallow modifications in the field, retrofit, etc. and provide a controlthat can adapt and provide the necessary PWM control signals, as well asprovide information to a user based on the detected configuration.

A dual stacked full bridge inverter circuit is shown in FIG. 4. SwitchesZ8,Z9,Z10,Z11 transformer T2 and diodes D9,D10 form the basic powercircuit for a first inverter circuit. Switches Z12,Z13,Z14,Z15transformer T3 and diodes D11,D12 form a second inverter circuit. Thesetwo circuits are arranged in a series arrangement on the input orprimary side with each connected across one half of the bus voltage(Vbus_top, Vbus_bottom). The output or secondary side is arranged in aparallel arrangement such that D9,D10 along with T2 share the outputcurrent with D11,D12 and T3. The switches are switched ON & OFF at aswitching frequency (ex. 20 Khz to 100 Khz) with a pulse width or dutycycle that is modulated to control and regulate the output currentand/or voltage as required to provide a welding type output. These pulsewidth modulation signals are indicated as PWM5, PWM6, PWM7 & PWM8. Thebasic operation of a full bridge circuit is well known and will not bedescribed further other than specific details as it relates to thecontrol of the PWM signals. Dual stacked inverter, as used herein, istwo stacked inverters connected in to have their outputs in parallel.Alternatives provide for a series connection, which will result in ahigher output voltage. The preferred embodiment has, on the input side,for a single inverter with there are 4 switches in series across the twoseries bus voltages with a single transformer. For a dual inverter, 4switches arranged in a full bridge driving the primary of onetransformer connected across each bus voltage with the two bus voltagesin series.

As with the stacked boost circuit, the stacked full bridge arrangementmay allow the use of lower voltage switches as the primary of eachinverter circuit operates from one half of the total bus voltage. Inaddition the stacked arrangement shown in FIG. 4 has some benefit inthat there is an inherent means to split and share the current on thesecondary and naturally force an approximate balancing of the two busvoltages on the primary (VBus_top & Vbus_bottom). For example if the topbus voltage is higher than the bottom bus voltage then the secondaryvoltage of T2 will be higher than the secondary voltage of T3 andtherefore T2 will take a greater proportion of the output current. Thisadditional current reflected to the primary of T2 means that the totalpower drawn from the top bus voltage will be greater than the powerdrawn by the lower inverter circuit on the bottom bus. This greaterpower will naturally decrease the top bus voltage relative to the totalbus voltage until an equilibrium point is reached. Thus there is passivebalancing or sharing. Active balancing or sharing may be desired forcertain dynamic or static load conditions such as for very small PWMvalues, such as during a short circuit condition on the output of thewelding type power supply. Active balancing of the top and bottom busvoltages may be performed independently or in conjunction with a voltagebalancing means implemented in the control for a single or dual stackedboost pre-regulator.

The inherent balancing of the series bus voltages, and sharing of outputcurrent may perform optimally with a small mismatch in the top andbottom bus voltages (ex. 2 to 3 volts difference), as naturally arrivedat by the tolerances of the various circuit components within theinverter circuit, switching characteristics, etc. As such it may bedesirable to disable active DC bus balancing within the pre-regulatorcircuit once the bus voltage difference falls below a limit (ex. within5 Volts differential).

In some arrangements of a welding, cutting or heating power supply thesecondary diodes D9, D10, D11 & D12 may be eliminated and the highfrequency AC of T2 & T3 used directly. Other arrangements may includefurther processing of the output power through an AC inverter circuit toprovide an AC output power with a frequency that may be independent ofthe inverter switching frequency and independent of the AC linefrequency. Any number of other additional circuits and controls may beprovided as required within a welding type system such as thermalsensors, fan control, user interfaces, weld process controls, datastorage, wire feeders, aux. power supplies, etc.

A stacked full bridge inverter circuit is shown in FIG. 5. The basicinverter circuit is comprised of switches Z8,Z9,Z14 & Z15 along withtransformer T2, blocking capacitor C4 and diodes D9,D10. SwitchesZ8,Z9,Z14 & Z15 are controlled by PWM signals PWM5, PWM6, PWM7 & PWM8.In this arrangement switches Z8 & Z15 are switched more or less togetherand switches Z9 & Z14 are switched ON and OFF together. Capacitor C4maintains a DC offset voltage approximately equal to one half Vbus. Ingeneral, operation of this arrangement of full bridge circuit is similarto the operation of one of the two full bridge inverter circuits shownin FIG. 4, with the main difference being that when switches Z9 & Z14are ON, the voltage across primary of T2 and thus the output power, issupplied by the voltage stored on blocking capacitor C4.

A basic system block diagram of the described welding type power supplyis shown in FIG. 6. AC line voltage is supplied to a rectifier circuitfollowed by a pre-regulator circuit. A regulated bus voltage (Vbus) isprovided by the pre-regulator to an inverter circuit, which in turnprovides a welding type power output. An aux. power circuit may also bepowered from the Vbus signal and provide an aux. power circuit. Forexample the aux. power circuit may provide 115 VAC in the form of arectangular waveform or a sine waveform or other suitable waveform. Theaux. power circuit may be used in a welding type system or cell to powervarious hand tools, grinders, fans, lights or other ancillary equipmentthat may be found in a weld cell. The aux. power circuit may or may notbe present in some welding type power supplies. A wire feeder powercircuit may also be powered from the Vbus signal and provide an outputpower signal for driving a wire feeder as part of a welding system. Thewire feeder power output may be a DC signal such as 42 VDC, or may be anAC signal in other systems. Again the wire feeder power circuit may ormay not be present in some welding type power supplies depending on theparticular configuration. Other similar power circuit such as forpowering a water cooler, heater, etc. may be provided in a similarfashion.

A control may receive input signals and/or provide various controlsignals to control the pre-regulator circuit, inverter circuit and anyadditional power circuits as shown in FIG. 6. These signals may includecurrent and voltage feedback signals, PWM signals, enable and statussignals, analog feedback signals, etc. In other words all of thenecessary signals as required to monitor and control the power circuits.The control may also interface to additional controls and/or circuitssuch as a weld control, user interface, etc. as required for properoperation of the welding type power supply within a welding operation.The control may be implemented using control circuits, microprocessorsand memory devices, software algorithms, or various combinations.

A pre-regulator control block diagram is shown in FIG. 7. Each of thefour switch circuits (Z4, Z5, Z6, & Z7) are provided with a PWM controlsignal generated by the pre-regulator control, and a detect signalprovided to the pre-regulator control to allow for the control to detectthe presence or lack of presence of the switch circuits. Each switchcircuit may contain a power semiconductor such as an IGBT, gate drivecircuit, thermal feedback, or other circuits. The detect signal may bean analog feedback signal or a logic signal that can be read or detectedby the pre-regulator control to sense the presence of each particularswitch circuit. As described above the pre-regulator control may alter acontrol sequence or algorithm based on the presence or lack of presenceof one or more of the switch circuits. For example if the controldetects the presence of four switch circuits then a current balancingcontrol may be implemented to balance the current flowing in the fourinductors shown in FIG. 2. Interface signals may be provide to a userinterface or other control to indicate the configuration of the weldingtype power supply. The switch detect signals may also be used to detectand indicate an abnormal situation or possible welding type power supplyfault. For example if the pre-regulator control detects the presence of3 of the 4 switch circuits, this may be indicated as a fault to theuser, and an indication provided as to which switch was not detected asan aid for servicing the welding type power supply.

Likewise the three current sensors may be connected to the control asshown to provide a current feedback signal indicative of the currentflowing in three of the inductors shown in FIG. 2. The current sensorsmay also provide a detect signal to the control, so that the presence orlack of presence of the current sensors can be detected. In apre-regulator circuit within a welding type power supply it is oftendesirable to control the pre-regulator current in some fashion, to limitthe current, to shape the current waveform to improve the power factor,to limit the input power or output power from the pre-regulator circuit,etc. Utilization of the current detect signal to modify the control ordisable operation if the current sensor is not detected can help assureproper operation, and/or assist with servicing of the welding type powersupply. Alternately the presence of the current sensors may be detectedby looking for a certain threshold of current feedback during operationor start up of the pre-regulator circuit. For example a start upsequence may operate the boost pre-regulator circuit for a certain timeperiod with a small PWM duty cycle value, such that the current cannotclimb too rapidly beyond a certain limit, yet allow detection that thesensor is providing a feedback signal. Alternately the expected currentfeedback signal may be calculated based on the input rectified voltagesupplied to the pre-regulator circuit, the output bus voltage, theswitch PWM duty cycle values and the inductor values, and this valuecompared to the actual current sensor feedback signals to determineproper operation of the current sensors. Additional signals not shownmay be provided to the current sensor circuit such as power supplies, orother signals required for proper operation.

The pre-regulator control may also be supplied with other signals suchas a feedback signal indicative of the rectified voltage(V_RECTIFIED_FEEDBACK) and bus voltage feedback signals(VBUS_TOP_FEEDBACK, VBUS_BOTTOM_FEEDBACK). These signals may be used toregulate the bus voltage, implement DC bus balancing between top andbottom bus voltages, detect a bus voltage unbalance and take some actionto correct or disable operation, verify proper input voltage based on adetected pre-regulator configuration, or other features and functions.The bus balancing is accomplished by a bus voltage balancing module thatreceives the bus voltage feedback signals, and causes the switches tooperate in such a way as to bring them closer together. Bus voltagebalancing module, as used herein, is a control module that controlsswitching signals so as to balance a bus voltage across multiplecapacitors.

Various interface signals may be provided to the inverter control, aux.power circuit, wire feeder power circuit, pre-charge circuit, and othercircuits within a welding type system. These interface signals may beprovided as outputs by the pre-regulator control or as inputs to thepre-regulator control. These interface signals allow for detection ofthe presence of certain circuits such as an aux. power circuit forexample and then to take some action based on the presence or lack ofpresence of certain circuits. For example if an aux. power circuit isdetected as present, then a power up routine for the aux. power circuitmay be activated as part of the overall power up routine of the weldingtype power supply. The aux. power circuit may be enabled for exampleonly after the pre-regulator has established Vbus at its nominalregulated value and determined that it is ok to enable the aux. powercircuit. After a certain power up time the pre-regulator control maythen verify operation of the aux. power circuit, and either continueoperation or disable operation depending on a detected status of theaux. power circuit. This status and operational information may becommunicated to a user via a user interface.

It may be desirable to limit the total input power or current to thewelding type power supply in some situations. As such it may bedesirable to reduce or limit the maximum welding type output power if anaux. power circuit is present. For example if an aux. power circuit thatcan provide up to 2 kw of output power is detected as part of theconfiguration of the welding type power supply it may be desirable insome situations to reduce the maximum welding output power by 2 kw orsome amount such that the input power does not exceed an upper limit. Inaddition it may be desirable to modify the control of a cooling fanbased on detecting the presence of an aux. power supply configuration,or based on an output power level of an aux. power supply. This mayallow for adequate cooling of aux. power supply components duringperiods when welding power output is at a reduced limit. The aux. powercircuit is detected in the manner described above for detecting othercircuits using an auxiliary power circuit detection module. Auxiliarypower circuit detection module, as used herein, is a control module thatdetects the presence of, or use of, an aux. power circuit.

The detection modules can provide configurations to a user-notificationmodule, which can notify the user of the configuration, or only notifythe user when there is an error detected. User-notification module, asused herein, is a control module that acts to notify the user of acondition or parameter.

A pre-charge circuit interface may also be provided to allow for the buscapacitors to be soft charged or pre-charged prior to operation of theboost circuit. A relay or AC line contactor, or other means as is wellknown may be used as part of a pre-charge circuit. The interface signalsmay contain additional information beyond detect, enable and status. Forexample DC bus voltage signals or information may be provided to theinverter control, such that the inverter control may take some action towork in conjunction with the pre-regulator control to force a DC busbalance. Any number of other signals may pass back and forth betweenthese and other parts of the welding type power supply. These signalsmay be in the form of hardware connections, variables in software,serial communication, or any other suitable form.

An example control circuit for a stacked boost pre-regulator circuitthat can accommodate a single or dual boost arrangement is shown in FIG.8. Circuit A1 is a bus voltage regulator circuit that provides an outputsignal to a boost current regulator circuit. The output of the busvoltage regulator circuit serves the purpose of regulating the total busvoltage to a fixed value (REF), based on feedback signals (VBUS_TOP &VBUS_BOT). For some welding type power supplies that require a range ofdynamic welding processes such as pulse welding it may be desirable totune the compensation network of the bus voltage regulator so that thepower flow out of the pre-regulator tends to be more responsive to theaverage welding power requirement and not the dynamic nature of thewelding process. This may require a compensation network that provides arelatively slow response (ex. 50 to 100 mSec).

Circuit A2 is a boost current regulator circuit that serves the purposeof regulating the boost current based on a current feedback signal(CS7). The output of the current regulator (I_ERROR) is read as ananalog input by a microprocessor and is used as one input to determine aPWM duty cycle for the four boost switches (PWM1-PWM4). For examplePWM1-PWM4 may be identical initially based on the value of I_ERROR.

Additional analog and digital inputs are provided to the microprocessor.These include analog current sensors signals (CS7, CS9 & CS10) thatprovide feedback information proportional to the current flowing in theinductors shown in FIG. 2. Analog bus voltage feedback signals(VBUS_TOP, VBUS_BOT) are also read by the microprocessor and may be usedas another input to modify a PWM duty cycle (PWM1-PWM4) to activelybalance the two DC bus voltages. A feedback signal representative of therectified voltage provided to the pre-regulator circuit by the inputrectifier (V_RECTIFIED) may also be provided. This feedback signal maybe used in various ways such as for detecting an input voltage that istoo high or too low for a particular pre-regulator configuration,detecting single phase power, etc. In some cases the rectified voltagefeedback may be used to modify the PWM values such that the inputcurrent is shaped and aligned with the input AC line voltage to furtherimprove power factor.

Z4-Z7 detect signals are provided to the microprocessor and may be usedto determine the boost configuration or arrangement (single or dual),and also detect an abnormal condition. Certain control and statusinformation is communicated with an inverter control via a serialcommunication circuit. Additional signals may be provided that are notshown such as rectified voltage feedback, thermal sensors, etc. Acircuit may alternately be inserted between the voltage regulator outputand the current regulator to provide further improved power factor byshaping the voltage regulator output to more closely follow the waveshape and alignment of the AC line voltage supplied to the rectifier. Amultiplier or other circuit may be used for this purpose.

The following illustrates one way the Z4-Z7 detect signals may be used:

1) Z4 & Z5 & Z6 & Z7 detected−configuration=DUAL BOOST

2) Z4 & Z5 detected−configuration=SINGLE BOOST

3) Any other combination detected=FAULT, disable boost and/or take otheraction.

A DC bus difference signal may be generated and utilized to generate abus balancing duty cycle term that can be used to modify one or more ofthe pre-regulator PWM signals. The following illustrates one method ofimplementing a DC bus balancing algorithm, taking into account thedetected configuration of the power circuit.

1) BUS_DIFF=Vbus_top−Vbus_bot

2) If magnitude BUS_DIFF>Fault_limit then FAULT, disable boost and/ortake other action.

3) If magnitude BUS_DIFF<Correction_lower_limit, then reset BUS_ERRORand disable bus balancing.

4) Otherwise accumulate a BUS_ERROR term: BUS_ERROR=BUS_ERROR+BUS_DIFF

5) If BUS_ERROR>0 this indicates top bus voltage is too high.

6) If configuration=DUAL BOOST, then PWM1=PWM1+K*BUS_ERROR,PWM3=PWM3+K*BUS_ERROR.

7) If configuration=SINGLE BOOST, then PWM1=PWM1+K*BUS_ERROR Similarlyif BUS_ERROR<0, this indicates bottom bus voltage is too high.

8) If configuration=DUAL BOOST, then PWM2=PWM2−K*BUS_ERROR,PWM4=PWM4−K*BUS_ERROR.

9) If configuration=SINGLE BOOST, then PWM2=PWM2−K*BUS_ERROR

A gain term or scaling term may be applied to BUS_ERROR (K) to providefor the correct scaling as applied to the PWM signals. Additionally themagnitude of BUS_ERROR may be limited to some upper limit, wherebyfurther accumulation of DC bus error is ignored. An accumulating buserror function or integrator may be desirable such that a largeBUS_ERROR term can be derived to force a large mismatch between upperand lower switch PWM values while maintaining a small magnitude of busvoltage difference.

In some situations such as at reduced output power levels of the weldingpower supply, the power output and current levels of the pre-regulatorcircuit are at relatively low levels. For these conditions and moreparticularly when the rectified input voltage is less than either thetop or bottom bus voltage it may be necessary to develop a largeBUS_ERROR term to effectively provide a bus balancing mechanism. Forother power levels and rectified voltage levels a small BUS_ERROR termmay effectively force a DC bus balance. Further DC bus correction may bedisabled once the bus voltage difference falls below a lower correctionlimit (ex. 5 Volts). This may be desirable to provide a means for theinverter circuit to arrive at a natural equilibrium operating point witha small bus voltage mismatch, as described above. In addition it may bedesirable to reset an accumulating bus error term or integrator so that,when bus balancing is once again required and activated within thepre-regulator control, the bus error term is not already at a anundesirable or incorrect value.

If the bus voltage difference is less than the fault_limit (ex. lessthan 50 Volts difference) but greater than a correction upper limit (ex.10 Volts difference), then a further DC bus correction scheme may beimplemented by communicating with the inverter control, such that theinverter control make take additional action to assist in balancing theDC bus voltages. One method is for the inverter control to increase thePWM duty cycles of the inverter that is operating on whichever DC bushas the greater magnitude. For example if the top bus voltage is toohigh relative to the bottom bus voltage then the inverter control mayincrease the PWM duty cycle of the upper inverter by some fixed orvariable duration (ex. 0.5 μsec). Once the magnitude of the DC busdifference falls back below an upper correction limit then this may becommunicated to the inverter control and this supplemental DC busbalancing disabled, or return the inverter PWM values back to theirnormal operating values. An alternative implementation may provide DCbus balancing coordination with an aux. power supply, control powersupply or other power circuit that can selectively draw more or lesspower from either the top or bottom bus.

A current balancing control system may also be implemented for a dualboost circuit to achieve current balancing in the four inductors asshown in FIG. 2. Current balancing may be desirable to actively forcethe 4 inductor currents (and subsequently the four switch currents) tomore or less match. Without active current balancing a mismatch in thefour currents can occur due to circuit differences and tolerances, (suchas gate drive, inductor differences, etc.) Again the pre-regulatorcontrol may utilize the detect signals (Z1-Z4) to detect a DUAL boostconfiguration and automatically implement the current balancing control.If a SINGLE boost configuration is detected then the current balancingportion of the pre-regulator control may be disabled. For SINGLE boostoperation there are only two inductors and the currents are naturallymatched.

In general current balancing is performed as follows. The two upperbranch currents (L7 & L9) are compared, the PWM value of whichever upperbranch has greater current is reduced by a value proportional to thecurrent difference. The two lower branch currents (L8 & L10) are thencompared, and the PWM value of whichever lower branch has greatercurrent is reduced by a value proportional to the current difference.The balancing of the two lower branch currents can be accomplished withonly one additional current sensor (CS10), by utilizing the fact thatthe sum of the two lower branch currents must equal the sum of the twoupper branch currents. Therefore the desired or target current for eachlower branch is one half of the sum of CS7 & CS9.

Alternately four current sensors could be utilized to determine the fourbranch currents. If DUAL BOOST:

1) Upper_current_error=CS7-CS9

2) If Upper_current_error>0 then PWM1=PWM1−K2*Upper_current_error

3) If Upper_current_error<0 then PWM3=PWM3+K2*Upper_current_error

4) Lower_current_error=(CS7+CS9)/2−CS10

5) If Lower_current_error>0 then PWM2=PWM2−K2*Lower_current_error

6) If Lower_current_error<0 then PWM4=PWM4+K2*Lower_current_error

Alternately the four branch currents could be controlled in a manner toactively force a percentage difference to account for differences incooling for example between the four different switches (Z1-Z4) or forother reasons. This could be accomplished by scaling the currentfeedback signals with different constants to force a percentagedifference. For example the Upper current error may be calculated asfollows:Upper_current_error=CS7−K3*CS9 (ex. K3=1.2)  1A)

This new Upper_current_error could then be used to adjust one of the twoupper PWM values (PWM1, PWM3) as before.

Likewise the two lower branch currents could be controlled in a similarfashion to force a percentage difference. The two lower branch currentsneed not be controlled with the same percentage difference as the twoupper. In this way the power circuit could be optimized based on aparticular power component and cooling arrangement.

Further alternatives could be utilized to actively balance the branchcurrents as described above, either to be the same or some percentagedifference. One alternative would be to provide one or more additionalboost current regulators as shown in FIG. 8, using the other currentfeedback signals (CS8, CS10). These additional current regulators couldbe connected to a common bus voltage regulator and used to generateadditional I_error signals, that could then be used as additional inputsto set the PWM signals.

Further modifications or limits may be applied to one or more of the PWMsignals for the pre-regulator (PWM1-PWM4). For example the duty cyclevalue may be clamped or limited to an absolute minimum or maximum value.Additionally a start up duty cycle limit may also be implemented so thatfor some duration as the pre-regulator is powering up and charging thebus voltage to its target value, the maximum duty cycle is furtherlimited. During this time interval the pre-regulator control may testthe values of CS7, CS8 and/or CS10 to determine if the current sensorsare providing valid feedback signals.

FIG. 9 shows a control loop model of a dual stacked boost pre-regulatorcircuit with a bus voltage balancing loop and upper and lower currentbalancing loops.

A bus voltage control loop sums feedback signals representing the topand bottom bus voltages. A gain factor is applied (K1) and the resultsubtracted from a reference or set voltage (Vref). The difference isapplied to a compensation network represented as G1(s) in the Laplacedomain. The output of the compensation network is a current referencecommand (Iref), that is an input to the master current control loop.Current feedback signal (CS7) is subtracted from Iref and applied to acurrent loop compensation network, G2(s). The output of the currentcontrol loop is an error signal (I_ERROR) which is used to set thevalues for the four PWM signals (PWM1-PWM4). Alternately another blockmay be inserted between the voltage control loop output (Iref) and thecurrent loop input to further improve the power factor by shaping theIref signal to more closely follow the shape and phase of the input ACvoltage. A multiplier function with the second input providing areference waveform indicative of the desired waveform may be used forthis function.

A bus balance control loop subtracts the bottom bus voltage feedbackfrom the top. The difference is applied to an integrator or compensationnetwork, G4(s). A limiter function limits the upper and/or lower limits.Switch SW1 applies the negative bus correction factor to the PWM signalsfor the lower switches (PWM2, PWM4). Switch SW2 applies a positive buscorrection factor to the PWM signals for the two upper switches (PWM1,PWM3). Switches SW1 &SW2 may remain disconnected whenever the busvoltage difference falls below a threshold.

A bottom current balance current control loop subtracts current feedbackCS10 from a target current value determined as the average of CS7 & CS9.A gain factor is applied (K3), and the result applied to a limiterfunction. The limiter may limit the upper and/or lower limits. SwitchSW3 applies a negative bottom current correction factor to PWM4 signal.Switch SW4 applies a positive bottom current correction factor to PWM2.The current balancing loops are part of a current balance module.Current balance module, as used herein, is a control module thatbalances current flow in multiple circuit paths.

A top current balance control loop subtracts feedback signals CS7 & CS9representing the two upper branch currents. A gain factor (K3) isapplied and the result applied to a limiter function. The limiter maylimit the upper and/or lower limits. Switch SW5 applies a negativebottom current correction factor to PWM3 signal. Switch SW6 applies apositive bottom current correction factor to PWM1.

A power up sequence may be implemented that is dependent on a detectedconfiguration. For example the power up sequence may be adapted based ondetecting the presence or lack of presence of an aux. power supply or awire feeder power supply. Likewise a power down sequence may be modifiedbased on a detected configuration. Start up module, as used herein, is acontrol module that acts to start a power circuit in a desired manner.Power down module, as used herein, is a control module that acts topower down a power circuit in a desired manner.

The following illustrates one possible power up sequence:

1) Pre-charge delay (allow initial charging of DC bus capacitors)

2) Self checks—verify SINGLE/DUAL boost configuration, verify currentsensor signals present, verify correct combination of Z1-Z4, etc.Improper configuration=FAULT, don't proceed with power up sequence.Other self-checks may be incorporated.

3) Verify Vbus_top, Vbus_bottom based on Vrectified. Each bus capacitorshould charge up to approximately ½ of Vrectified for example.

4) Enable Pre-charge relay or contactor to bypass a pre-charge resistor.

5) Enable boost pre-regulator circuit, soft-start mode (limit maximumPWM duty cycle, maximum current, etc.).

6) Boost delay time

7) Verify boosted DC bus voltage (Vbus_top, Vbus_bot)

8) If aux. power circuit detected:

8A) Enable aux. power circuit.

8B) Aux. power up delay.

8C) Aux. power circuit verification (is it operating properly), if notthen disable and indicate to user and/or take other action.

8D) Calculate maximum power available for weld power output based onpower consumed by aux. power.

9) If wire feeder power circuit detected:

9A) Enable wire feeder power circuit.

9B) Wire feeder power circuit delay for power up.

9C) Wire feeder power circuit verification (is it operating properly),if not then disable and indicate to user and/or take other action.

10) Enable inverter circuit to provide welding power output.

An inverter control block diagram is shown in FIG. 10. The switchcircuits (Z8-Z15) are provided with PWM control signals to control theduty cycle of the switches based on various inputs and controls toeffectively generate a welding type power output. The switch circuitsmay be grouped as shown or individually, and provide one or more detectsignals to the inverter control. These detect signals may be used in asimilar fashion as was described for the pre-regulator control. Forexample combinations of certain detect signals could indicate a dualstacked full bridge power configuration as shown in FIG. 4, or a stackedfull bridge configuration as shown in FIG. 5. As such the invertercontrol may modify how the PWM signals are generated are controlledbased on this detected configuration. Abnormal combinations of detectsignals could generate a fault that disables operation of the invertercircuit. This fault could be communicated to the pre-regulator controlto take further action such as disabling the pre-regulator circuit.

The inverter control may also be supplied with current and voltagefeedback or other feedback signals as required to generate a weldingtype power output. A weld control for example may require certaincurrent or voltage waveforms to produce a weld. The inverter control mayuse the feedback signals to produce the required waveforms. Additionalinterface signals may be provided to communicate with other componentswithin the welding type power supply or system as required, such as weldcontrol, user interface, pre-regulator control, etc.

In addition a fan control signal may be generated to control one or morecooling fans. The fan control signal may be modified or controlled basedon a detected arrangement of the inverter power circuit, and/or thepre-regulator circuit. For example a dual stacked boost may be detectedfor the pre-regulator circuit, and a dual stacked full bridge circuitdetected for the inverter. Based on this detected configuration a fanmay be operated at a maximum speed. For another configuration the fanmay be operated at a slower speed. An AC fan (ex. 115 VAC) may be usedfor cooling, and the speed controlled by varying the frequency of thevoltage supplied to the fan (Ex. 50 Hz for slow, 60 Hz for fast). ThisAC signal may be synthesized by a well known AC H-bridge circuit orother similar circuit. In addition or alternately the speed or controlof the fan may be modified based on other inputs such as a currentfeedback signal (CS1 for example), a thermal sensor, ambient temperatureor other inputs.

A simplified inverter control circuit is shown in FIG. 11. Circuit A3 isa current regulator circuit that accepts a reference signal (REF) and acurrent feedback signal (CS1) and generates an error signal (I_ERROR).The reference signal may be generated by a weld process control or othermeans and provide a set level or reference welding waveform that isresponsive to conditions in the welding arc. Some welding processes arevery dynamic with complex reference waveforms and arc conditions thatcan vary rapidly from a short circuit to an open arc condition. As suchthe current regulator is normally fast enough to respond to the requiredchanges to produce a desirable weld condition. As such the error signal(I_ERROR) may vary rapidly as required to control the PWM signals forthe inverter switches and thus control the output of the inverter.

A microprocessor may read the analog value of I_ERROR and act upon it togenerate the necessary PWM signals. Four unique PWM signals may berequired to control the dual stacked full bridge inverter circuit.Various other analog and digital signals may interface with themicroprocessor as required to control the inverter as well as interfacewith the other components within the welding type power supply orsystem. Z8-Z15 detect signals may be incorporated as described above todetect a power circuit configuration, or abnormal condition. In additionan interface may be provided to the boost pre-regulator control. Thisinterface may provide information or signals to coordinate DC busbalancing in conjunction with DC bus balancing actions performed by theboost pre-regulator control. In some situations as described above, itmay be desirable for the inverter control to take action to assist inmaintaining a DC bus balance. Additional signals, control and circuitsnot shown may be incorporated such as a fan control as described above.

The inverter control circuit generates four PWM signals as indicated inFIG. 12. The PWM signals control the switches (Z8-Z15) as shown in FIGS.4 & 5. Each PWM signal has a switching frequency or period (T_PERIOD)and a duty cycle (D) representing the time duration that the switchesare turned on. Two of the PWM signals are phase staggered by one halfthe switching period. It can be seen from FIGS. 4 & 5 that PWM5 & PWM7apply a voltage (VBUS_TOP, VBUS_BOTTOM) across the primaries of theinverter transformers (T2, T3) in one polarity, and that PWM6 & PWM8apply the same voltages in an opposite polarity. A magnetic flux isgenerated in each transformer in proportion to the applied voltage andduty cycle of the PWM signals. As is well known it is desirable that thevolt*sec product that is applied across the transformer in one polaritybe balanced with the volt*sec product applied in the opposite polarity,otherwise transformer saturation can occur. Because of the phasestaggered nature of these opposite polarity pulses and the dynamicnature of a welding arc or process, the duty cycle or PWM values areoften changing from one cycle to the next. The control shown in FIG. 11,may implement a flux balancing algorithm to reduce the likelihood oftransformer saturation by keeping track of the net time or duty cyclevalue applied in each polarity and limiting the PWM duty cycle value foreither polarity if a flux limit is exceeded.

A model of an inverter control loop illustrating a flux limitingfunction as well as a DC bus balancing function is shown in FIG. 13. Amaster current control loop generates an error signal (I_ERROR) inresponse to a reference signal or command (REF) and a current feedbacksignal indicative of the output current of the welding type power supply(CS1). The master current control loop may contain a compensationcircuit or function (G2(s)) to tailor the dynamic characteristics of thecontrol loop and provide stability. The error signal is used to generatea positive polarity PWM signal, which ultimately controls PWM5 and PWM7,and a negative polarity PWM signal which controls PWM6 & PWM8. Positiveand negative being arbitrary descriptors of the polarity of the voltageapplied across the primaries of the transformers (T2,T3). These PWMsignals may be generated by discrete sampling of the error signal, or bya continuous function such as a PWM ramp comparator.

A flux accumulator or integrator is shown which keeps a history of thenet flux or volt*sec that has been applied to the transformers. Ineffect it only is necessary to keep track of the PWM values due to thenature of the regulated bus voltage provided as an output of thepre-regulator. Alternately the bus voltage could be measured and thisused as an input to the flux accumulator. The net flux is calculated byadding the positive PWM value and subtracting the negative PWM value, toa running accumulator. If the flux value or in this case net PWM valueexceeds a positive threshold then a limiter may be applied to limit themaximum value of the positive PWM value as shown. Likewise if the netPWM value exceeds a negative threshold then a limiter may be applied tolimit the maximum value of the negative PWM value as shown.

A DC bus correction duty cycle term (D_BUS_CORRECTION) may beselectively added to the two PWM signals (PWM5, PWM6) that control theupper inverter on the top bus, or added to the two PWM signals (PWM7,PWM8) that control the lower inverter on the bottom bus. This DC buscorrection term may be added in coordination with the pre-regulatorcontrol to assist with DC bus balancing for certain conditions, such asmay occur for small PWM values for PWM5-PWM8. For example as describedfor the pre-regulator control, if a DC bus imbalance is less than afirst limit, bus correction may be disabled. If DC bus imbalance exceedsthis first limit then the pre-regulator may take action to balance theDC bus voltages as described. If the DC bus imbalance exceeds a secondlimit then a signal may be communicated to the inverter control and thebus correction term applied to either the upper or lower inverter PWMsignals (D_BUS_CORRECTION). If the DC bus imbalance exceeds a thirdlimit then both the inverter and pre-regulator may be disabled or otheraction taken. The DC bus correction term applied to the inverter PWMsignals may be a fixed duty cycle term or may be set in proportion orsome other relation to the magnitude of the imbalance. In general thisbus correction term may be limited to a relatively small percentage ofthe PWM signal.

The stacked boost configuration may be further extended to a triple, ormore, boost circuit arrangement with current balancing implemented in asimilar fashion as described. For example a target current could bedetermined for each of the upper inductors or current branches bycalculating or measuring the total current and dividing by the number ofboost circuits in the arrangement.

Alternative inverter topologies such as a stacked forward, half bridge,flyback or other topology could be used. In addition in someconfigurations of a welding type power supply it may be desirable to usea single inverter circuit operating from the total bus voltage, ratherthan a stacked or series arrangement of inverter circuits while stillusing some of the features and advantages of the pre-regulator circuitas described.

Other pre-regulator and/or inverter control schemes are also possiblesuch as variable frequency, fixed on time, fixed off time, frequencydithering, or various combinations as alternative or in conjunction withthe PWM schemes described.

Alternative inverter topologies such as a stacked forward, half bridge,flyback or other topology could be used. In addition in someconfigurations of a welding type power supply it may be desirable to usea single inverter circuit operating from the total bus voltage, ratherthan a stacked or series arrangement of inverter circuits while stillusing some of the features and advantages of the pre-regulator circuitas described.

Other pre-regulator and/or inverter control schemes are also possiblesuch as variable frequency, fixed on time, fixed off time, frequencydithering, or various combinations as alternative or in conjunction withthe PWM schemes described.

Numerous modifications may be made to the method and system which stillfall within the intended scope hereof. Thus, it should be apparent thatthere has been provided a method and apparatus for providing weldingtype power that fully satisfies the objectives and advantages set forthabove. Although the method and system have been described in conjunctionwith specific embodiments thereof, it is evident that many alternatives,modifications and variations will be apparent to those skilled in theart. Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

The invention claimed is:
 1. A welding-type power supply comprising: acontroller, having a preregulator control output and an output convertercontrol output, wherein the controller comprises a bus voltage balancingmodule and the preregulator control output is responsive to the busvoltage balancing module; a preregulator disposed to receive a range ofinputs voltages and to receive the preregulator control output, and toprovide a preregulator output signal, wherein the preregulator includesa plurality of stacked boost circuits; a preregulator bus, disposed toreceive the preregulator output signal; and an output converter,disposed to receive the preregulator bus and to receive the outputconverter control output, and to provide a welding type power output. 2.The welding-type power supply of claim 1, wherein the preregulator busis voltage regulated.
 3. The welding-type power supply of claim 1,wherein the output converter includes a dual stacked inverter.
 4. Thewelding-type power supply of claim 1, wherein the plurality of stackedboost circuits is a dual stacked boost circuit.
 5. The welding-typepower supply of claim 1, wherein the bus voltage balancing moduleincludes at least one of an integrator and an accumulator.
 6. Thewelding-type power supply of claim 1, wherein the bus voltage balancingmodule receives feedback from the pre-regulator and output converter. 7.The welding-type power supply of claim 4, wherein the controllercomprises a current balance module.
 8. The welding-type power supply ofclaim 1, wherein the controller comprises an output converter fluxbalancing module.
 9. The welding-type power supply of claim 1, whereinthe controller comprises a start up module and a power down module. 10.The welding-type power supply of claim 1, wherein the controllercomprises a power circuit configuration detection module, and wherein atleast one of the preregulator control output and the output convertercontrol output is responsive to the power circuit configurationdetection module.
 11. The welding-type power supply of claim 1, furthercomprising a user-notification module responsive to the power circuitconfiguration detection module and an auxiliary power circuit detectionmodule.
 12. The welding-type power supply of claim 1, furthercomprising: a synthetic auxiliary ac power circuit having an acadjustable frequency auxiliary power output; and a variable speedcooling fan disposed to blow air toward at least part of thepreregulator and the output converter, and disposed to receive theauxiliary power output.
 13. A welding-type power supply comprising: acontroller, having a preregulator control output, an output convertercontrol output, a bus voltage balancing module, wherein the preregulatorcontrol output is responsive to the bus voltage balancing module; apreregulator disposed to receive a range of inputs voltages and toreceive the preregulator control output, and to provide a preregulatoroutput signal and to provide feedback to the bus voltage balancingmodule; a preregulator bus, disposed to receive the preregulator outputsignal and an output converter, disposed to receive the preregulator busand to receive the output converter control output, and to provide awelding type power output.
 14. The welding-type power supply of claim13, wherein the bus voltage balancing module includes at least one of anintegrator and an accumulator.
 15. The welding-type power supply ofclaim 14, wherein the controller comprises a current balance module. 16.The welding-type power supply of claim 15, wherein the controllercomprises an output converter flux balancing module.
 17. Thewelding-type power supply of claim 16, wherein the controller comprisesa start up module and a power down module.
 18. The welding-type powersupply of claim 16, wherein the controller comprises a power circuitconfiguration detection module, and wherein at least one of thepreregulator control output and the output converter control output isresponsive to the power circuit configuration detection module.
 19. Thewelding-type power supply of claim 18, further comprising: a syntheticauxiliary ac power circuit having an ac adjustable frequency auxiliarypower output; and a variable speed cooling fan disposed to blow airtoward at least part of the preregulator and the output converter, anddisposed to receive the auxiliary power output.